Photographic silver halide emulsion



i in relatively high potential developers.

. my invention into Patented Feb. 1s, 1943 PHOTOGRAPBIC SILVER HALIDEEMULSION Walter J. Weyerts, Rochester, N. Y., assignor to Eastman KodakCompany, Rochester, N. Y.,`a corporation of New Jersey ApplicationNovember 13, 1941, Serial No. 418,952

This invention relates to sensitive photographic emulsions, and moreparticularly to a method for improving the sensitometric characteristicsof y such emulsions.

Salts in light-sensitive. silver halide emulsion layers have'long been asubject of discussion in the art. It has long been a practice to washphotographic emulsions to free them of salts formed during emulsionmaking, for instance, in

order to increase the sensitivity of the emulsions.

On the other hand, salts of acids such as acetic. adipic, etc., havebeen used as buffers in emulsions with beneficial results. l

I have found that if salts of the organic Iacids of my invention areused in sunicient quantities in emulsions they improve the sensitometriccharacteristics of the emulsions, such as gamma and speed. 'I'hus theaddition of soluble salts of organic acids to photographic emulsionscauses an increase in the development rate. This is particularly truewhen these emulsions are developed Therefore, for a given time ofdevelopment an increase in gamma, and often an increase in eifectivespeed as well, is obtained with emulsions containing such addenda. Onthe other hand. for development to equal gammes. an emulsion coat-i ingcontaining an addendum as above will require s, shorter time ofdevelopment than a similar emulsion. coated without any addendum.Furthermore, it has been found that these salts cause an increase ingamma infinity and the maximum densityl that is obtained on developmentof the exposed emulsion.

It is, therefore, the object of the present inven- 'tion to provideorganic acid salts which may be stitution products. such as the aminobenzene sulfonic acids--metanilic, sulfanilic and orthanilic:

1o claims. (ci. tis-'1) salt in Water,I and addlngfthis lsolution withor without the addition of an organic solvent such as alcohol, to theemulsion at some stage in its manufacture. A convenient method is to addthe salt solution to a melted gelatin-silver-halide emulsion Just priortof coating. As cations for the salts I may use bases furnishingammonium, amine or alkali metal ions.

I have found that the quantity of'salt used in an. emulsion is acritical factor in therrespect that if too little is used, itssensitometric characteristics such as gamma and speed will not beappreciably affected. lThe following data show'the effect of usingvarying quantities of sodium acetate, based on the amount of gelatin, ina sensitized emulsion. Development was for the same time in a highpotential developer. Y

Percent sodium acetate H10/i speedA Gamma Fog uw 0. 92 07 955 l. 39 05um 1. 19 06 1010 l. 11 06 Thus, if the salt is present in an amount suchas is customarily used in buffer solutions, that is, less than about 5per cent of the weight of the gelatin, little or no change insensitometric characteristics will be observed when such an emulsion iscompared with a control emulsion containing-no salt. The quantity I useis from yabout 5 per cent-25 per cent, preferably about l5 per cent,

' of the weight of the carrier material. if gelatin is benzoic acid andits substitution products, such as -anthranilic and Vsalicylic acids.Other substitution products of benzene carboxylic and sulfonic acids,such as o. m or p-bromobenzoic, o, m or p-chlorobensoic and2,5-dichlorobenzenesulfonic are likewise effective.

The method I use for incorporating the salts ofthsacidfurnishingtherequiredanioninalkaline solution or dissolving therequired pre-formed emulsions, consists of dissolving used.' Similarquantities may be used 'for emulsions having carriers other than'gelatin.

The effect of the salts on emulsion characteristics is better understoodby reference to the accompanying drawing. wherein Figs. 1, 2, 3, and 4show by graphical representation the en'ect of typical salts onsensitometric characteristics such as gamma and speed.

In the drawing, Iiig. l shows by means of H and D curves, thesensitometric characteristicsof a non-color sensitized bromoiodidecontrol emulsion before addition of sodium glycolate, and after the salthas'been added' (l5 per cent salt on the weight of gelatin). Bothemulsions were vgiven the same time of development in a high potentialdeveloper. It is lobserved that if the straight-line portion of thecurves are extended to the abscissa, a comparison of the gamma and speedmay be made. It is apparent that in this case the salt has beeninstrumental in causing an increase in both speed and gamma.

Fig. 2 shows the effect of adding 15 per cent of the weight of gelatinof sodium metanilate to a high-speed emulsion. It may be seen that thegamma and speed of the treated emulsion. as shown by the curve to theleft, is considerably higher than that of the control emulsion.

Fig. 3 shows the H and D curves of two emulsions, to one of which hasbeen added 15 per cent sodium 'anthranilata The effect of the additionof the salt to theemulsion is to produce a considerable increase ingamma and an increase in speed which is not as great in the toe regionas it is along the straight-line portion of the curve, as calculated byWell-known methods which recognize that at the same inertia speedsdifferent gammas give at the same density different speeds, such asastronomical speeds. A

Fig. 4 illustrates in a similar manner the eiect of adding sodiumacetate to an emulsion. The particular'control emulsion, the H and Dcurve of which is shown at the right in the ilgure, was an opticallysensitized emulsion having a /i speed'of 1070, gamma 1.03, and fog. .08.When sodium acetate was added in the amount of 40 per cent of the weightof the gelatin to the control emulsion, the speed was 1200gamma 1.39 andfog .09. Development was carried out in a high potential developer forthe same time in each case.

Example 10/i speed Gamma Fog Control 525 l. 25 05 570 1. 50 06 640 l. 3205 510 1. 49 08 550 l. 43 07 545 l. 47 05 590 1. 73 06 Ammonium benzoate575 l. 65 06 It is to be noted that the l0/i method of obtainingemulsions speeds (as described in Shepherd U. S. Patent 2,184,023,granted December 19, 1939) is subject to certain limitations and is notapplicable in all cases to give a clear picture of the effect o! saltsgiving curves such as shown in Fig. 2 and Fig. 3. Other methods whichrecognize that at the same inertia speeds different gammas give at thesame density different speeds, such as astronomical speeds, are moresuitable. Computations made by these methods show that in the regions ofhigher density there are speed diiferences between two given emulsions,whereas, the 10/i method might show little or no difference in speeds.

I have found that the eifect of the salts in my invention on emulsioncharacteristics is not limited to a specific type of emulsion. Emulsionswhether non-sensitized, optically or chemically sensitized, arefavorably affected. 'I'he salts differ somewhat in their ability toimprove sensitometric characteristics. For instance, the same controlemulsion was used for the experiments the results of which are shown inFig. 2 and Fig. 3, and it is apparent that the improvement in gamma andspeed is different in each case. The same is true of isomeric salts suchas sodium metanilate and sodium sulfanilate. Similarly, differentsubstitution products of the salts of the acids of my invention givediilerent types and degrees of improvement of sensitometriccharacteristics of emulsions. Simple experiments illustrate the eifectof such salts on emulsion characteristics.

It is to be understood that the disclosure herein is by way of exampleand that I consider as included in my invention all modications andequivalents falling within the scope of the appended claims.

What I claim is:

l. 'Ihe method of improving the sensitometric characteristics of agelatine-silver halide emulsion which comprises treating said emulsionwith a salt having a cation selected from the group consisting ofammonium, amino and alkali metal, and an anion of an aliphatic hydroxymonobasic organic acid.

2. 'I'he method of increasing the gamma of a gelatina-silverhalideemulsion which comprises treating said emulsion with a salt having acation selection from the group consisting of ammonium, amino and alkalimetal, and an anion of an aliphatic hydroxy monobasic organic acid.

3. lThe method of increasing the gamma of a gelatine-silver halideemulsion which comprises treating said emulsion with a water-solublesalt of glycolic acid.

4. The method of increasing the speed of a gelatino-silver halideemulsion which comprises treating said emulsion with a salt having ac'ation.selected from the group consisting of ammonium, amino and alkalimetal, and an anion of an aliphatic hydroxy monobasic organic acid.

5. The method of increasing the speed of a gelatine-silver halideemulsion which comprises treating said emulsion with a salt having acation selected from the group consisting of ammonium, amino and alkalimetal, and an anion from lactic acid.

6. The method of increasing the gamma and speed of a gelatino-silverhalide emulsion which comprises treating said emulsion with a salthaving a cation selected from the group consisting of ammonium, aminoand alkali metal, and an anion of an aliphatic hydroxy monobasic organicacid. a

'1. The method of increasing the gamma and speed of a gelatino-silverhalide emulsion which comprises treating said emulsion with an alkalimetal salt of glycolic acid.

8. A silver halide emulsion comprising as an agent for improving thesensitometric characteristics thereof, a salt having a cation selectedfrom the group 'consisting of ammonium, amino and alkali metal, and ananion of an aliphatic hydroxy monobasic organic acid.

9. A silver halide emulsion comprising as an agent for increasing thegamma thereof. a wa-

